1. Field of the Invention
The present invention relates to electronic circuit units having a circulator in which a central conductor to be placed in a magnetic field is mounted in a circuit board.
2. Description of the Related Art
A conventional circulator S2 will be described below with reference to FIGS. 14 and 15. The circulator S2 is formed of a plurality of laminated dielectric substrates 52 having three central conductors 51 arranged at intervals of 120 degrees and disposed so as to partially intersect each other, a magnet 53 and a ferrite member (not shown) disposed above and below the intersection of the central conductors 51, a first yoke 54 made from a magnetic member and disposed so as to cover the outside of the magnet 53 above the intersection, and a second yoke 55 made from a magnetic member, connected to the first yoke 54, and disposed so as to cover the outside of the ferrite member positioned below the intersection.
In the circulator S2, the first and second yokes 54 and 55 form a closed magnetic circuit. Input and output terminals 51a are provided for the three central conductors 51 and protrude toward the outside from the side faces of the first and second yokes 54 and 55. The circulator S2 is thus formed as a single product.
A circuit board 56 serving as an antenna combining unit is provided with a hole 56a and a plurality of electrically conductive patterns 57 disposed around the hole 56a. On the circuit board 56, various electric components (not shown) are mounted to form a desired electronic circuit.
The circulator S2, formed as a single product, is positioned in the hole 56a of the circuit board 56, and the terminals 51a of the central conductors 51 and a ground electrode (not shown) are placed on electrically conductive patterns 57 and connected thereto by soldering or other methods. An electronic circuit unit having the conventional circulator is thereby formed.
In the circulator having the above-described structure, a signal input to any of the input and output terminals is output from another input and output terminal disposed in one rotation direction, but is not output from another input and output terminal disposed in the opposite rotation direction. This phenomenon is called the Faraday effect.
In the electronic circuit unit having the conventional circulator, since the circulator S2 is formed as a single product and is soldered to the circuit board 56, the electronic circuit unit is costly to manufacture, needs a large space on the circuit board, and has a large overall size.
Moreover, and as shown in FIG. 16, since the central conductors are opposed to each other through dielectric substrates, distributed large-capacitive components C are formed among the central conductors at intersection points P. Therefore, the central conductors are coupled with each other by the distributed capacitive components C. An equivalent circuit shown in FIG. 17 is generated between an input and output terminal and the next input and output terminal disposed in the opposite rotation side, to which a signal is not to be output, and a signal is actually output through a distributed capacitive component C.
Accordingly, it is an object of the present invention to provide a compact electronic circuit unit having a circulator that is manufactured with high productivity to reduce the level of an output signal leaked to an input and output terminal to which the signal is not to be output by the Faraday effect.
The foregoing object is achieved in one aspect of the present invention through the provision of an electronic circuit unit having a circulator, including a circuit board which is obtained by laminating a plurality of dielectric substrates and in which an electric component is provided to form a desired electronic circuit. First, second, and third central conductors are provided on the circuit board and partially intersect with each other in the upper and lower directions. A magnet and a ferrite member are disposed above and below the intersection of the central conductors. A first yoke covers the outside of the magnet, and a second yoke covers the outside of the ferrite member. Wherein the first, second, and third central conductors are provided for a plurality of dielectric substrates and formed by laminating the plurality of dielectric substrates; a cavity for accommodating the ferrite member is provided at a lower section of the circuit board in which the central conductors are disposed; a plurality of through holes vertically passing through the circuit board are filled with a magnetic material; and a magnetic path is formed by the magnetic material between the first and second yokes disposed above and below the circuit board so as to cover the magnet and the ferrite member, to make a closed magnetic circuit.
The magnetic material may be formed by filling the through holes with a paste including a magnetic powder.
The electronic circuit unit having a circulator may be configured such that at least one of the first and second yokes has a cylindrical side wall, and the dielectric substrate is provided with a ring-shaped magnetic pattern which opposes the end section of the side wall and which is connected to the magnetic material.
The magnetic pattern may be provided for each of the dielectric substrates positioned between the first and second yokes.
The electronic circuit unit having a circulator may be configured such that the ferrite member is disposed in the cavity; the magnet is disposed on the upper surface of the circuit board; the first yoke having the cylindrical side wall is disposed so as to cover the outside of the magnet; and the second yoke having a plane shape is disposed so as to cover the outside of the ferrite member and to block the cavity.
The electronic circuit unit having a circulator may be configured such that an electrically conductive pattern is provided on the front surface of a first-layer dielectric substrate disposed at the top of the circuit board; the first, second, and third central conductors are provided for dielectric substrates disposed below the first-layer dielectric substrate; and one end of each of the first, second, and third central conductors is connected to the electrically conductive pattern by a through-hole conductor provided in the circuit board.
The other end of each of the first, second, and third central conductors may be grounded through a through-hole conductor provided in the circuit board at a position closer to the center than the ring-shaped magnetic pattern.
The through-hole conductor connected to the other end of each of the first, second, and third central conductors may be connected to one highly electrically conductive member.
The electronic circuit unit having a circulator may be configured such that a capacitor for the circulator is provided on the upper surface of the circuit board by printing at a position outside the first yoke, and the capacitor can be trimmed after the first yoke has been mounted.
The foregoing object is achieved in another aspect of the present invention through the provision of an electronic circuit unit having a circulator, including a circuit board obtained by laminating a plurality of dielectric substrates. First, second, and third central conductors are provided for the plurality of dielectric substrates at intervals of 120 degrees and partially intersecting with each other in the upper and lower directions. A magnet and a ferrite member are disposed above and below the intersection of the central conductors. A first yoke covers the outside of the magnet, and a second yoke covers the outside of the ferrite member. Wherein one end of each of the first, second, and third central conductors serves as an input and output terminal, the ends being disposed at intervals of 120 degrees, and adjacent input and output terminals are connected by inductive elements.
The electronic circuit unit having a circulator may be configured such that electrically conductive patterns connected to the input and output terminals, and microstriplines for connecting the electrically conductive patterns, are provided on the circuit board. The microstriplines are formed of the inductive elements.
The resonant frequency of a parallel resonant circuit formed of the inductive elements and capacitive components generated between the central conductors by the intersections of the central conductors may be made equal to the frequency of a signal input to an input and output terminal.